This invention relates to a method and device for cell culture sampling in suspension cell culture vessels.
The in vitro growth of animal cells as cell cultures is a widely developed art. In recent years there has been a trend in the cell culture field toward growing these cells in suspension culture. Background information on this trend can be had be reference to U.S. Pat. No. 3,850,748 and references cited therein.
For a variety of reasons, there is a need to take frequent cell culture samplings during growth of animal cells in suspension culture. Various parameters of the cell culture growth conditions need to be monitored such as, for example, determination of the condition of the cells and the culture medium components, estimation of the cell density, and assay of products being released into the culture medium. Similar samplings need to be made during storage of cell culture media to ensure the integrity of the media.
Critical to any cell culture system is the maintenance of absolute sterility. Since the taking of samples from cell culture vessels provides an ideal source of microbial contamination, special precautions must be observed during any sampling procedure. A common method of attacking the problem of microbial contamination is to employ high levels of antibiotics in the cell culture medium. The use of antibiotics, however, detrimentally affects cell metabolism and cell products by masking chronic low level contamination, by stimulating the development of resistant microorganisms and by introducing uncontrolled variables into the cell culture process. Consequently, a method of sampling which can be carried out without need to employ antibiotics in the culture medium would have much practical use.
Another approach used for maintaining a sterile environment during cell culture sampling is to carry out the sampling procedure in a biological laminar flow hood. However, this means is useful only for relatively small vessels and is not adaptable to large scale culture vessels.
Sampling procedures used in the microbiological fermentation field have also been adapted for use in cell culture system. In the fermentation field, sampling techniques have been developed in which the sample is withdrawn with a sterile hypodermic needle inserted through a pierceable and self-resealable, elastomeric septum in an appropriately placed sampling port of the fermentation vessel. Such techniques are illustrated, for example, in U.S. Pat. No. 3,075,888. However, this technique is suitable for piercing at each hole only once and is not generally adaptable to repeated samplings in cell culture systems. The inherent risk in repeated use of such procedures in the cell culture field is apparent from the fact that a mammaliam cell culture contaminated by even a single microorganism may be rapidly overgrown and destroyed since the doubling times for mammalian cells are from 50 to 500 times larger than for common microorganisms. This cell culture contamination problem differs significantly from what occurs in the ordinary fermentation field where the proliferation rate of likely microbial contaminants is on the same order as that of the desired culture. A single or even a few contaminating microorganisms do not overgrow the desired fermentation culture and thus are not observed.